safety and immunogenicity study of booster vaccination with medium-dosage or high-dosage sars-cov-2 inactivated vaccine for prevention of covid-19

Conditions: COVID-19

Summary: this is a randomized, double-blinded, phase ⅰv clinical trial of sars-cov-2 inactivated vaccine manufactured by manufactured by sinovac research \& development co., ltd. the purpose of this study is to evaluate the safety and immunogenicity of booster vaccination with high-dosage sars-cov-2 vaccine in populations who have received two-dose coronavac with 2nd dose vaccinated more than 6 month.

this study a randomized, double-blinded, phase ⅰv clinical trial of sars-cov-2 inactivated vaccine .the purpose of this study is to evaluate the safety and immunogenicity of booster vaccination with high-dosage sars-cov-2 vaccine in populations who have received two-dose coronavac with 2nd dose vaccinated more than 6 month.a total of 1200 subjects who have received two-dose coronavac with 2nd dose vaccinated more than 6 month will be enrolled.all of subjects will be randomly divided into two groups in a 1:1 ratio .subjects in experimental group will receive high-dosage sars-cov-2 inactivated vaccine.subjects in control group will receive medium-dosage sars-cov-2 inactivated vaccine .

Eligibility criteria:
inclusion criteria: * adults aged 18-59; * proven legal identity; * the subjects can understand and voluntarily sign the informed consent form and be willing to complete the study in accordance with the study plan; * have received two doses of inactivated sars-cov-2 vaccine(coronavac) manufactured by sinovac research \& development co., ltd at an interval of 21 to 35 days and is currently 6-8 months (180 to 240 days) after the second dose. exclusion criteria: * history of sars-cov-2 infection(laboratory confirmed); * have received three and more doses of inactivated sars-cov-2 vaccine; * severe adverse reactions, such as urticaria, dyspnea, and angioneurotic edema , occurred during the primary immunization; * autoimmune disease such as systemic lupus erythematosus or immunodeficiency / immunosuppression such as aids, post-transplant; * severe chronic diseases, severe cardiovascular diseases, hypertension and diabetes that cannot be controlled by drugs, liver or kidney diseases, malignant tumors, etc; * severe neurological disease (epilepsy, convulsions or convulsions) or mental illness; * diagnosed abnormal blood coagulation function (eg, lack of blood coagulation factors, blood coagulopathy, abnormal platelets) or obvious bruising or blood coagulation; * immunosuppressive therapy, cytotoxic therapy, inhaled corticosteroids(excluding allergic rhinitis corticosteroid spray therapy, acute noncomplicated dermatitis superficial corticosteroid therapy) in the past 6 months; * history of alcohol or drug abuse; * receipt of blood products within in the past 3 months; * receipt of other investigational drugs in the past 30 days; * receipt of attenuated live vaccines in the past 14 days; * acute diseases or acute exacerbation of chronic diseases within 7 days prior to booster vaccination; * axillary temperature \>37.0°c; * already pregnant or are breastfeeding, planning to get pregnant within 1months (according to subjects' self-report and urine pregnancy test results); * participated in other clinical trials prior to enrollment and during the follow-up period, or planned to participate in other clinical trials during the clinical trial period; * according to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.